I�ve fished many bodies of water where dead fish were visibly present so I�m not saying it doesn�t happen, but there is always a cause. Sometimes pollution, sometimes a hard freeze, aeration or oxygen/carbon dioxide levels,, overheating, choking trying to eat a fish or bird that was too big lol etc..
I�m def no expert but start with getting your water tested. And not just for the basic PH, alkalinity, salinity, ammonia, nitrates, nitrites, etc.. you might send it into a lab to get a full analysis on what�s happening bc you shouldn�t be seeing fish just die off regularly.
